The majority of mothers in Ireland provide formula milk to their infants during the initial weeks postpartum; however, data are lacking on their formula feeding practices and support needs. This prospective Dublin-based observational study, which included 450 eligible mother-term infant pairs recruited and followed up to six months postpartum, aimed to advance our understanding of maternal formula feeding practices, their reasons for deciding to formula feed, sources of feeding information and perceived support needs; insights into infant formula milk consumption patterns in relation to current feeding guidelines are also provided. In summary, the vast majority of infants at six weeks were provided with formula milk (n =368; 81.8%). Positive maternal perceptions of formula feeding were among the most frequently reported reasons underlying mothers' decisions to formula feed (e.g. convenience, 17.3%). Potential public health concerns over the large formula milk volumes consumed by infants (mean 205 ml/kg/day) relative to infant feeding guidelines (150 ml/kg/day) were raised from this study. Some mothers continue to add solid foods to infant bottle feeds at six weeks (3.8%) and six months (6%), a non-recommended feeding practice posing a choking risk for infants. Crucially, this study highlights the need to provide greater support and information to mothers who decide to formula feed postpartum, including practical information on sterilisation and formula reconstitution. While breastfeeding promotion and research continues to be a public health priority in Ireland, addressing the support and information needs of mothers who formula feed, an under-represented and understudied population in the literature, also needs to be considered to ensure optimal health and safety for their infants. (Contains 5 tables.)